TIPS
Feb 21, 2008
One-Gyro Science On-Orbit Test
&
Kalman Filter Sunpoint Safemode Test
Merle Reinhart
1
TIPS
Feb 21, 2008
What is 1-Gyro Science Mode?
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•
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In this mode, only 1 gyro is available for rate sensing
Now have a gyro-less plane rather than just a gyro-less axis as 2gyro mode
Has three main sub-modes like 2-gyro mode
– M1G - Attitude errors can be as large as 9 degrees
» Sensors are:
• The Gyro
• Magnetic Sensing System
• Coarse Sun Sensor
» A Kalman Filter which is an attitude predictor-corrector is used to
combine all the sensors along with aerodynamic and gravity gradient
torque compensations to provide for a 3-axis stabilized control.
– T1G - Attitude errors can be as large as a few tens of arcseconds
» Sensors are:
• The Gyro
• Fixed Head Star Trackers
» Perform OnBoard Attitude Determinations to reduce the attitude errors
– F1G - Attitude errors typical at the catalog error of about 0.3 arcseconds
» Sensors are:
• The Gyro
• The Dominant FGS
2
TIPS
Feb 21, 2008
Why 1-Gyro Science Mode?
• SM4 is only 27 weeks away. Why are we still talking about 1Gyro mode?
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Gyro run times (21-Feb-2008)
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•
G1 49850 hours (5.69 yrs)
- operational, powered
G2 57411 hours (6.55 yrs)
- failed 31-Aug-2007, flex lead
G3 33197 hours (3.79 yrs)
- failed 29-Apr-2003, rotor restriction
G4 53505 hours (6.10 yrs)
- operational, turned off 28-Aug-2005
G5 16126 hours (1.84 yrs)
- failed 28-Apr-2001, rotor restriction
G6 16723 hours (1.91 yrs)
- operational, powered
Mean time to flex lead failures is 41800 (4.77 yrs) hours
All 6 gyros (3 rate sensing units - RSUs) are slated to be replaced
during SM4 in EVA2
3
TIPS
Feb 21, 2008
Gyro Lifetime Estimates
•
Chart below shows approximate gyro failure probabilities assuming a gyro failure in July
2007 (close to time of Gyro #2 failure)
1
0.9
SM4
0.8
Jul-2007
Availability
0.7
0.6
Feb-2011
Jan-2009
0.5
0.4
0.3
May-2008
0.2
0.1
0
Feb-2007
Feb-2008
Feb-2009
Feb-2010
Feb-2011
Feb-2012
Feb-2013
Feb-2014
Feb-2015
Tim e (calendar date)
1 or more operating gyros
2 or more operating gyros
3 gyros (2 operating, 1 in-reserve)
Predictions from Helen Wong (Aerospace Corp)
as communicated to Art Whipple (HSTP)
4
Feb-2016
Feb-2017
TIPS
Feb 21, 2008
The OGS On-Orbit Test
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Visits from 4 proposals
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11077 - WFPC2
11078 - Astrometry
11497 - Mars
11345 - PCS Tests
5
OGS Test was a full 2 days
KFSP Test was 18 hours
Total time 2d 21h
TIPS
Feb 21, 2008
OGS High Level Results
• Completed OGS on orbit testing
– Assessment indicates performance as expected
• 60/60 OBADs with nominal performance
– Max correction for 1st OBAD was 2.44 degrees and 2nd OBAD
was 38 arcsec
• 18/18 guide star acquisitions/reacquisitions were successful
– Astrometry, 2-GS with re-acq, 1-GS with re-acq, K13 variations,
Mars
6
TIPS
Feb 21, 2008
F1G OOT Performance
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Jitter computed over entire guiding interval with merged data
Values shown are the 60 second root sum squared of the V2 and V3 standard
deviations of position path
Data Start
Time
FGSs In
Use
Dominant mV,
catalog
Max Jitter,
DVTHEP, mas
Mean Jitter,
DVTHEP, mas
Min Jitter,
DVTHEP, mas
Comments
29/17:03
2,3,3
13.124
7.0
5.8
5.0
Astrometry
29/18:39
2,3,3
13.523
9.7
6.6
5.8
Astrometry
29/20:15
2,3,2
13.837
9.2
7.4
6.6
Astrometry
29/21:51
1,2,2
13.693
8.6
7.0
6.4
WFPC2
29/23:34
2,3,3
13.477
9.9
6.8
6.0
WFPC2
30/01:11
2,3,3
13.477
8.9
6.8
6.0
WFPC2
30/02:46
2,3,3
13.477
7.2
6.4
5.8
Reacq
30/04:22
2,3,2
13.864
7.6
7.1
6.7
WFPC2
30/05:58
2,3,2
13.864
8.3
7.2
6.7
WFPC2
30/07:34
1,3,1
12.914
6.5
5.7
4.9
WFPC2
30/09:09
1,3,1
12.914
5.8
5.2
4.8
WFPC2
30/10:45
2,1,2
11.955
3.6
3.1
2.7
Mars
30/15:24
2,0,2
13.144
7.7
6.6
5.9
Ast/1FGS
30/16:54
2,0,2
13.144
5.7
5.3
5.0
Reacq/1FGS
31/02:38
2,3,3
13.970
7.7
7.0
6.5
Acq test
31/04:13
2,3,3
13.970
8.4
7.3
6.5
Acq test
31/05:49
2,3,3
13.970
7.5
7.1
6.6
Acq test
31:08:52
2,3,3
13.991
7.9
7.2
6.6
Astrometry
Note that the DVTHEP jitter during persistent disturbances from simulations is ~2-3 mas larger than science
7
instrument jitter for faint stars
TIPS
Feb 21, 2008
New Kalman Filter Sun-Point Safemode
• The Safe Mode Flow Down
Science Mode
Inertial Hold
Kalman
Filter
Sunpoint
Zero Gyro
Sunpoint
PSEA
Hardware
Sunpoint
8
TIPS
Feb 21, 2008
KFSP Performance
• Design Goals were for better performance than ZGSP
• KFSP performance met ALL expectations
– Entries into orbit day following captures during orbit night had
no discernable attitude errors
– Captures had minimal overshoots
– Slews to the sun-line appeared to be pure eigenvector maneuvers
– No noticeable rates about the sun-line after capture
• One of the major advantages of KFSP over ZGSP is that the
attitude is held even at night such that the aperture door is
not required to be closed
9